1. Field of the Invention
The present invention relates to a magnetoresistance effect device for reading a signal of magnetic field strength from a magnetic medium, and a magnetoresistance effect film for use in the device. More particularly, the present invention relates to a magnetoresistance effect film for generating a larger output under a smaller external magnetic field.
2. Description of the Related Art
A magnetoresistance(MR) sensor or head has been known in the art as a magnetic reading transcducer that can read data with a larger linear density from a magnetic surface. The MR sensor detects a magnetic field through a resistance variation that is a function of an intensity and direction of a magnetic flux sensed by a magnetic reading device. Such a conventional MR sensor operates on the basis of the anisotropic magnetoresistance (AMR) effect. The AMR effect is known to vary one component of a resistance in the magnetic reading device proportional to the square of cosine of an angle between the magnetization direction of the device and the direction of a sense current flowing through the device. D. A. Thompson et al., xe2x80x9cMemory, Storage and Related Applicationsxe2x80x9d, IEEE Trans. on Mag., MAG-11, P.1039 (1975) describes the AMR effect in more details.
A further recent report demonstrates a more remarkable MR effect that can cause resistance variations in a laminated magnetic sensor due to the spin-dependent transmission of conduction electrons between magnetic layers via a non-magnetic layer and due to the accompanying spin-dependent scattering at the interfaces thereof. This MR effect is called with various names such as xe2x80x9cgiant magnetoresistive effectxe2x80x9d, xe2x80x9cspin valve effectxe2x80x9d, etc. This MR sensor is composed of appropriate materials and has a more improved recording density and larger resistance variation than that of the AMR sensor. In a plane between a pair of ferromagnetic layers that are isolated by a non-magnetic layer in such an MR sensor, a resistance varies proportionally to the cosine of an angle between the magnetization directions of the two ferromagnetic layers.
JP-2651015(B2) publication discloses a laminated magnetic structure that causes a high MR variation due to the anti-parallel arrangement of magnetization between magnetic layers. The publication exemplifies transition metals and alloys as materials useful for the ferromagnetic layers in the laminated structure. It also discloses a structure that includes an antiferromagnetic layer, appropriately FeMn layer, added onto one of at least two ferromagnetic layers isolated by an intermediate layer.
JP-8-21166(B2) discloses another MR sensor that includes two thin film layers of ferromagnetic material separated by a thin film layer of non-magnetic metal. At no magnetic field application, the magnetization directions of the two ferromagnetic thin film layers cross at right angle with each other. A resistance between the two uncoupled ferromagnetic layers varies proportional to cosine of an angle between the magnetization directions of the two layers and is independent of the direction of a current flowing through the sensor.
Although these MR devices can work in a small magnetic field, they have a disadvantage because of a low Neel temperature of FeMn and poor thermal stability when they are employed for practical sensors and magnetic heads.
The use of high Neel temperature PtMn, PdMn and NiMn for the ferromagnetic thin film requires an appropriate heating process to obtain an antiferromagnetic phase. This heating process causes the disadvantage of reducing the resistance variation rate, which is the output from the device.
Thinning the magnetic layer to increase the device sensitivity to the magnetic field, elevates the resistance due to the effect of electron scattering on the surface of the MR film and accordingly reduces the MR effect, lowering the output.
An object of the present invention is to provide a magnetoresistance effect film and device capable of exhibiting a large resistance variation linearly at near zero magnetic field with an excellent thermal stability.
According to the present invention, there is also provided a magnetoresistance effect film on a substrate, which comprises a plurality of magnetic thin films, a non-magnetic thin film disposed between the magnetic thin films, and an antiferromagnetic thin film arranged adjacent to one of a pair of magnetic thin films laminated via a non-magnetic layer. The antiferromagnetic thin film has an exchange bias field of Hr. The other of the pair of magnetic-thin films has a coercive force of Hc2 lower than Hr. The magnetoresistance effect film further comprises a ground layer formed on the substrate. The antiferromagnetic thin film is laminated adjacent to the ground layer. Material of the ground layer is selected from the group consisting of a nickel oxide, a cobalt oxide, an iron oxide and an alloy composed of at least two selected therefrom. Material of the antiferromagnetic thin film is selected from the group consisting of PtMn, PdMn, NiMn and an alloy composed of at least two selected therefrom. The antiferromagnetic thin film has a surface with an average roughness 1-5 xc3x85.
According to the present invention, there is also provided a magnetoresistance effect film on a substrate, which comprises a plurality of magnetic thin films, a non-magnetic thin film disposed between the magnetic thin films, and an antiferromagnetic thin film arranged adjacent to one of a pair of magnetic thin films laminated via a non-magnetic layer. The antiferromagnetic thin film has an exchange bias field of Hr. The other of the pair of magnetic thin films has a coercive force of Hc2 lower than Hr. The magnetoresistance effect film further comprises a ground layer formed on the substrate. The antiferromagnetic thin film is laminated adjacent to the ground layer. Material of the ground layer is selected from the group consisting of a nickel oxide, a cobalt oxide, an iron oxide and an alloy composed of at least two selected therefrom. Matereial of the antiferromagnetic thin film is selected from the group consisting of PtMn, PdMn, NiMn and an alloy composed of at least two selected therefrom. The antiferromagnetic thin film has a surface with an average roughness of 1-5 xc3x85.